Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

2. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Freon

Brine

3. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

4. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

5. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 3

1: 9

6. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

7. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Room air conditioners

Domestic refrigerators

8. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

Superheat the vapour

10. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Positive

Negative

Page 2 of 4

11. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

12. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

13. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

14. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

15. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

16. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

17. In a lithium bromide absorption refrigeration system

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

18. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Toxic

19. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

20. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always less than unity

Always more than unity

Page 3 of 4

21. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

22. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

None of these

Sub-cooling or under-cooling

23. Rating of a domestic refrigerator is of the order of

5 tons

0.1 ton

10 tons

40 tons

24. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

25. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

26. Which of the following cycles uses air as the refrigerant?

Carnot

Stirling

Bell Coleman

Ericson

27. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

28. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

29. The boiling point of ammonia is

-77.7°C

-30°C

-33.3°C

-10.5°C

30. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

Page 4 of 4

31. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.4

0.376

32. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

33. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

34. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

35. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Piston type reciprocating

Axial

36. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

37. For obtaining high COP, the pressure range of compressor should be

Any value

Optimum

High

Low

38. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

Capillary tubes

39. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

2 bar

15 bar

30 bar

40. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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